The use of tumour-selective prodrugs (relatively inactive compounds that can be selectively converted to more active compounds in vivo) is a valuable concept in cancer therapy.
For example a prodrug may be converted into an anti-tumour agent under the influence of an enzyme that is linkable to a monoclonal antibody that will bind to a tumour associated antigen. The combination of such a prodrug with such an enzyme monoclonal/antibody conjugate represents a very powerful clinical agent. This approach to cancer therapy, often referred to as “antibody directed enzyme/prodrug therapy” (ADEPT), is disclosed in W088/07378.
A further therapeutic approach termed “virus-directed enzyme prodrug therapy” (VDEPT) has been proposed as a method for treating tumour cells in patients using prodrugs. Tumour cells are targeted with a viral vector carrying a gene encoding an enzyme capable of activating a prodrug. The gene may be transcriptionally regulated by tissue specific promoter or enhancer sequences. The viral vector enters tumour cells and expresses the enzyme, in order that a prodrug is converted to an active drug within the tumour cells (Huber et al., Proc. Natl. Acad. Sci. USA (1991) 88, 8039). Alternatively, non-viral methods for the delivery of genes have been used. Such methods include calcium phosphate co-precipitation, microinjection, liposomes, direct DNA uptake, and receptor-mediated DNA transfer. These are reviewed in Morgan & French, Annu. Rev. Biochem, 1993, 62; 191. The term “GDEPT” (gene-directed enzyme prodrug therapy) is used to include both viral and non-viral delivery systems.
4-Nitroaromatic compounds are reduced by both mammalian and bacterial flavoprotein enzymes, which effect stepwise addition of up to six electrons. The major enzymic metabolite is usually the 4-electron species (hydroxylamine).
The present invention relates to novel nitroaniline-based unsymmetrical mustards having cytotoxic activity, to methods of preparing the novel compounds, and to the use of these compounds as prodrugs for GDEPT and for cell ablation therapy in conjunction with nitroreductase enzymes (particularly the nitro reductases encoded by the nfsB gene of E. coli or by Clostridia species), as hypoxia-selective cytotoxins, and as anticancer agents.
Both dinitrobenzamide aziridines (e.g., 1) [Knox et al., Cancer Met. Rev., 1993, 12, 195] and nitro- and dinitrobenzamide mustards (e.g., 2-4) [Friedlos et al., J. Med. Chem., 1997, 40, 1270] have been reported as substrates for the aerobic E. coli nitroreductase (NTR), and as specific prodrugs for GDEPT in conjunction with NTR.

Unsymmetrical (chloro-mesylate) mustards have been reported [e.g., Marais et al., Cancer Res. 1996, 56, 4735], including the dinitro analogue 5 [Friedlos et al., J. Med. Chem. 1997, 40, 1270], which was described as not sufficiently potent for a full biological evaluation to be conducted.
It is therefore an object of the invention to provide a series of unsymmetrical mustards, methods for preparing the unsymmetrical mustards that are suitable for use as prodrugs for GDEPT (gene-dependent enzyme-prodrug therapy) and cell ablation therapy in conjunction with nitroreductase enzymes, as hypoxia-selective cytotoxins, and as anticancer agents or to at least provide the public with a useful alternative.